A conventional X-ray CT scanner has a gantry holding an X-ray tube and a detector. The gantry has a stationary part which is standing at or mounted to the floor of a hospital room. Furthermore, it has a rotating part held by a bearing at the stationary part. The rotating part holds the X-ray tube and the X-ray detector at opposing positions, and allows rotation thereof around a patient table on which a patient may be positioned. For specific types of imaging, at least the rotating part of the gantry may be tilted against parts of the stationary part and against the patient table.
A general CT scanner is disclosed in the U.S. Pat. No. 6,301,324. A tiltable rotating part of a gantry is disclosed in the U.S. Pat. No. 6,097,030. Here a detector position sensor, such as a decoder is coupled to a tilt drive servo motor and configured to generate signals representative of the detector tilt angle. The drawback of this embodiment is a very complex decoder and the requirement of a position reference of detector tilt. Furthermore a decoder calibration may be required when powering on the CT scanner. A decoder has to be mounted and aligned. A relative decoder requires a zero position search after power on and thus a disadvantageous movement of the tilt gantry. A decoder as disclosed in U.S. Pat. No. 6,097,030 is often called encoder or rotary encoder.